The present invention relates to flexible pipe couplings in general, and more particularly to improvements in flexible pipe couplings of the type wherein an elastic sleeve which can consist of rubber or an equivalent material surrounds the end portions of the pipes which are to be coupled to each other and is surrounded by a clamp serving to bias the internal surface of the sleeve against the external surfaces of the end portions of the pipes.
The aforementioned commonly owned copending patent application Ser. No. 664,346 discloses a flexible pipe couling wherein the sleeve has a ring-shaped partition which extends from its internal surface and between the end faces of the two pipes and the clamp includes a band in the form of a split ring with L-shaped projections at its ends. The first leg of each projection is bonded to the external surface of the respective end of the split ring, and the second leg of each projection extends radially outwardly from the split ring and has a hole for the shank of a bolt which mates with a nut and is used to move the second legs of the two projections nearer to each other in order to tighten the split ring around the elastic sleeve. The marginal portions of the split ring slope toward the external surfaces of the respective pipes and overlie the respective open ends of the sleeve, and the central portion of the split ring is formed with a corrugation which extends into a groove in the external surface of the sleeve.
The flexible pipe coupling which is disclosed in the copending patent application Ser. No. 664,346 can be used with advantage to establish a fluidtight connection between drain pipes which consist of cast iron. The L-shaped projections of its clamp consist of sheet metal and are welded to the split ring. The clamp is intended to tighten the sleeve around the end portions of the pipe with a force which suffices to ensure that the sleeve can withstand substantial stresses tending to move the two pipes substantially axially and away from each other, i.e., to extract the end portions of the pipes from the sleeve. It has been found that the ability of a pipe coupling with L-shaped projections at the ends of the split ring to resist extraction of the end portions of the pipes from the sleeve is rather limited, primarily because the second legs of the L-shaped projections tend to bend in response to rotation of the nut and shank relative to each other in order to reduce the distance between the second legs and such bending takes place before the split ring can clamp the sleeve with a force which is required to ensure that the sleeve is held in requisite frictional engagement with the external surfaces of the pipes. The thickness and strength of the L-shaped projections cannot be increased at will, not only because this would contribute to the bulk, weight and cost of the clamp but also because the first legs of relatively thick projections cannot be readily spot welded to the respective ends of the split ring. Spot welding is the currently preferred mode of bonding the projections to the split ring. Still further, relatively thick, heavy, stiff and bulky projections would adversely influence the ability of the split ring to ensure the establishment of a reliable seal between the two pipes during bending of the sleeve, i.e., on movement of one of the pipes to a position in which its axis is inclined with reference to the axis of the other pipe. More specifically, relatively heavy and thick projections would prevent the aforementioned corrugation of the split ring from compensating for eventual tolerances in the outer diameters of the pipes, and such heavy and thick projections would further prevent adequate flexing of the sleeve under the above outlined circumstances, i.e., when the axis of one of the pipes which are coupled to each other is inclined with reference to the axis of the other pipe.
The tightening or clamping force which is furnished by the bolt and nut and is applied to the central portions of the second legs is transmitted primarily or to a larger extent to the marginal portions of the split ring diametrically opposite the two projections. The marginal portions are bent inwardly toward the external surfaces of the respective pipes and they apply to the sleeve radial forces which are greater in the region diametrically opposite the projections than at the end portions of the split ring. Such non-uniform distribution of radial forces, as considered in the circumferential direction of the marginal portions of the split ring, reduces the reliability of the clamp as concerns its ability to resist axial stresses, i.e., a movement of the end portions of the pipes away from each other. Premature bending of the second legs relative to the first legs of the projections in response to tightening of the clamp around the sleeve is undesirable because the second legs are likely to come into actual abutment with each other, and to thus prevent further tightening of the clamp around the sleeve, before the sleeve undergoes a deformation which suffices to prevent leakage of the conveyed fluid and/or ready extraction of the end portions of the pipes from the sleeve. Non-uniform distribution of radial forces, as considered in the circumferential direction of the marginal portions of the split ring, is undesirable on the ground that this reduces the likelihood of the establishment of a predictable and reliable seal between the internal surface of the sleeve and the external surfaces of the pipes, on the ground that it prevents the sleeve from furnishing an adequate sealing action when one of the pipes is moved to a position in which its axis is inclined relative to the axis of the other pipe, and on the ground that the pipes can be readily moved axially and away from each other, e.g., in response to increasing pressure of the confined fluid medium. The likelihood of unsatisfactory sealing action and/or insufficient resistance of the sleeve to axial movements of the pipes away from each other is especially pronounced when the clamp employs a single bolt and nut and when the width of the band-shaped split ring is relatively small, e.g., in the range of between 35 and 50 mm.